Preferred pre-stimulus EEG states affect cognitive event-related potentials
Current views of the genesis of the event-related potential (ERP) emphasize the contribution of ongoing oscillations — the ongoing electroencephalogram (EEG) is recognized as much more than “background noise” to be removed by response averaging to find the ERP. Early work from Başar's group noted that repetitive stimuli led to selective phase re-ordering of activity in the delta and alpha bands, such that enhanced brain negativity occurred at the time of the regular stimulus. Other work related negativity in alpha activity at stimulus onset to improved reaction times and ERP enhancements. These findings led us to begin a program of brain dynamics studies exploring pre-stimulus EEG phase states, their preferential occurrence in paradigms with regularly presented stimuli, and their relation to ERP outcomes. In particular, with very narrow EEG bands, we have repeatedly found that certain phase states preferentially occur at stimulus onset, implying ongoing phase re-ordering driven by stimulus occurrence. Effects are weakened with slightly varying inter-stimulus intervals, but still occur reliably. Further, these preferential phase states are functionally effective in relation to the ERP correlates of efficient stimulus processing. Preferential phase occurrence and their effects were originally reported in auditory oddball tasks, using narrow EEG bands derived by digital filtering. A recent study is presented illustrating generalization of the phenomenon in the auditory Go/NoGo task, using narrow bands derived by FFT techniques. Our current work is extending this research in normal children (to provide a comparative context for research in children with AD/HD), and well-functioning elderly (to provide a context for future work in relation to Alzheimer's disease).